Methods of chemical nickel plating



D. E. METHENY ETAL 2,874,073

METHODS oF CHEMICAL NICKEL PLATINC Feb, 17,l 1959 2 Sheets-Sheet 1 Filed Nov. 7, 1957 SSQ ESQ, m ESG n SE m AT S EQQ Ew@ m S SE n SEQ uw C :N n 5mm Q SEQ W Mw m? R n R SENS SE1 m wm Su: lm QMQQl @www ww wm m m umwnw su Q @Low k. NMO@ Y N N A SE SS SQ w m E N Sm@ wk Wiss@ N m G, m En@ NQ JUN u .Smm Q s n KE 9% /uv w EQ @ER /\|m vm VN V\ t N j@ N\ w? mm ENG EQQ r sm m QQ S man wm SS@ mw N Km uw 3 E Si Feb. 17, 1959 D. E. METHENY ETAL METHODS oF CHEMICAL. NICKEL PLATIN@ 2 Sheets-Sheet 2 Filed Nov. 7, 1957 Fig 2v my mmf .NMU W W WV o m .w 5 En ,am 8 wm .Q\

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r l EE "United States Patent O 2,874,07 3 METHODS F CHEMICAL NICKEL PLATING Application November 7, 1957, Serial No. 695,128

21 claims. (C1. 117-130) The present invention relates to methods of chemical nickel plating, and more particularly to continuous plating methods of the general character of that disclosed in U. S. PatentfNo. 2,717,218, granted on September 6, 1955 to Paul Talmey and William I. Crehan.

in the operation of a continuous chemical nickel plating system of the character of that disclosed in the Talmey and Crehan patent, there is some slight random chemical nickel plating upon the walls of the plating tank and the other component parts thereof that are in direct contact with the hot chemical nickel plating solution of the nickel cation-hypophosphite anion type, notwithstanding the fabrication that are not ordinarily catalytic to the nickel reductionhypophosphite oxidation reaction, whereby it is necessary periodically to remove the random nickel deposit from the surfaces of these parts, and otherwise to clean these surfaces. Of course, this is necessary, since thereaction mentioned is autocatalytic, whereby the principal reaction proceeds directly upon any layer of random nickel plating carried by these surfaces.

Accordingly, it is a general object of the present inof these parts from materials vention to provide an improved continuous chemical nickel plating method, wherein random nickel plating upon the plating tankV and other component parts of the system is avoided.

Another object of the invention is to provide an improved combination of method that substantially completely eliminates random nickel .plating in the systemand that greatly simplifies the operation and control of the plating process.

Further featuresof the invention pertain to the particular arrangement of the steps of the chemical plating method, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best following specification taken in connection with the accompanying drawings, in which:

Figure l is a diagrammatic illustration of a system for chemical nickel plating in which the method of the present invention may be carried out; and

Fig. 2 is a graphic illustration of the relationship between the plating rate and the lead ion concentration in an l exemplary chemical nickel plating bath of the nickel cation-hypophosphite anion type.

At the outset, it is pointed out that the present invention is predicated upon the discovery that the conjoint control of a plurality of factors involved in the continuous chemical nickel plating process can be made so as substantially completely to eliminate the undesirable random nickel plating upon the surfaces of the plating tank and of the other component parts of the system in direct contact with the hot chemical nickel plating solution of the nickel cation-hypophosphite anion type. More parsteps in the chemical plating be understood by reference to the ticularly, in order toobtain the desired result aforesaid, p

L 2,874,073 Patented Feb. 17, 1959 ICC it is first necessary to fabricate the plating tank essentially of steel containing a high chromium content (for example, stainless steel) and periodically to deactivate the steel walls of the plating tank by treatment with a dilute nitric acid solution. In the second place, it is necessary that the hot bath of the plating solution in the plating tank be at a temperature not in excess of C. In the third place, the plating solution must contain a stabilizing amount of a stabilizer (such, for example, as lead ion) therein, in the range of parts-per-million of the plating solution by weight and corresponding to the maximum stabilizer concentration therein that is compatible with both a high plating rate of the plating bath and complete plating coverage of the work-pieces that are to be plated therein.

The stabilizer mentioned is of the character of that disclosed in U. S. Patent No. 2,763,723, granted on September 1l, 1956 to Paul Talmey and Gregoire Gutzeit; which stabilizer inhibits random decomposition of the plating bath. While a wide variety of stabilizing agentsv may be employed, as disclosed in the Talmey and-Gutzeit patent, the three principal groups of these agents comprise heavy metal ions (for example, lead ions), inorganic thio compounds (for example, thiosulfate), and organic thio compounds (for example, potassium ethyl xanthate). More fundamentally, these stabilizing agents comprise catalytic poisons for the dehydrogenation reaction that proceeds in the bath at the surfaces of the catalytic work-pieces that are being plated.

This will best be understood when it is considered that the overall nickel reduction-hypophosphite oxidation that occurs at the surface of the catalytic Work-piece and in the plating bath, infact involves several individual reactions:

Thus the hypophosphite ion is dehydrogenated at the catalytic surface to produce the metaphosphite ion; and active hydrogen that is adsorbed on the catalytic surface Equation I. Simultaneously, the metaphosphite ion rel acts with water to produce the orthophosphite ion Equation II. Some of the active hydrogen on the catalytic surface then reduces the nickel ion thereat, producing the useful metallic nickel deposit upon the catalytic surface, and is simultaneously oxidized, producing the increase in the hydrogen ion concentration in the bath as the process proceeds Equation Ill. Other of the active hydrogen on the catalytic surface forms molecular hydrogen, producing the gaseous hydrogen that appears upon the catalytic surface Equation IV.

Since these stabilizer agents are catalytic poisons (negative catalyst) for the catalytic dehydrogenation reaction of Equation I, they control the formation of atomic hydrogen for use in Equation III, thereby controlling the rate of the plating upon the catalytic surface.

As disclosed in the Talmey and Gutzeit patent, it is a normal characteristic of these chemical nickel plating baths that the plating rate of an unmoditedplating bath is increased by the addition thereto of a small amount of the stabilizing agent (ordinarily in parts-per-million of the bath by Weight), and is then depressed somewhat by the further addition thereto of a similar small amount of the stabilizing agent, and is then substantially depressed by the still furtheraddition thereto of a similar small amount of the stabilizing agent. Moreover, the different plating baths of this type are peculiarly sensitive to a particular stabilizing agent with respect to the plating rate theredof; ile., different ones ofthe plating baths have substantially different tolerances for ya particular stabilizing agent. Furthermore, a given plating bath of this type is peculiarly sensitive to the different ones of the stabilizing agents with respect to the plating 'rate thereof; i. e., the given plating Abath has substantially different tolerances for the different ones of the stabilizing agents.

Now in accordance with the previously noted step in the present method, a particular stabilizing agent is selected and added to a given plating bath in an amount `that ismin excess of the amount required to achieve a maximum plating rate of the plating bath, and that is suiiicient .toneffect a depression of about 5% to 10% in the rmaximum plating rate of the plating bath. For example, when lead ion is employed as the stabilizing agentvfor a given plating bath, the stabilizing amount Iof'lead ions required is ordinarily in the range from l to 5 p. p. m. of 'the bath by weight and generally corresponds to a lead ion concentration in the bath of about V2 p. p. m. above the lead ionconc'entration therein that is productive of the maximum plating rate thereof.

Referring now to Fig. l of the drawings, there is diagrammatically illustrated a continuous chemical nickel plating system that is suitable for carrying out the method of the present invention; which system essentially comprises a regeneration tank 10, a storage tank 11, a heater 12,V a pair of plating tanks 13 and 14, a cooler 16, two liquid pumps 17 and 18, a first pair of filters 20 and 21 and a second pair of filters 22 and 23, as well asa pair of boats 24 and 25 respectively operatively associated with the plating tanks 13 and 14. In the arrangement, the heater 12, the plating tanks 13 and 14, the cooler 16, and the pumps 17 and 18 are formed essentially of steel having a high chromium content, for example, ordinary stainless steel S302, S304, S318, etc.; at least the parts of the Velements named that are in contact with the'chemical nickel plating solution are fabricated of stainless steel.

The storage tank 11 is Vadapted to contain the chemical nickel plating solution,V and the outlet thereof is connected to a conduit 31 provided with two branches, one of the branches extending to drain and including a valve 32, and the other of the branches extending to the inlet of the pump 17 and including a valve 33. The filters and 21 are arranged between two headers 34 and 35; While the filters 22 and 23 are arranged between the header 35 and a header 36. The header 34 may be directly connected to the header 35 by a valve 37; and

the header 35 may be directly connected to the header 36 byy avalve 38. The lter 29 may be selectively connected between the headers 34 and 35 by two valves 41 and 42; the filter 21 may be selectively connected between the headers 34 and 35 by two valves 43 and 44; ythe filter 22 may be selectively connected between the :headers 35 and 36 by two valves 45 and 46; and the filter 23 may-be selectively connected between the headers 35 and 36 by two valves 47 and 48. The outlet of the pump 17 is connected to the header 34, and the outlet of the .header 36 is connected to a conduit 41 that is provided with two branches, one of the branches extending to drain and including a valve 42, and the other of the branches extending to an inlet header 61 of the heater 12 and including a valve 43.

The iilter 26 may be isolated from the circulation system by closure of the valves 41 and 42 and is pro- Vvided with a vdrain conduit including a valve 51; the filter 21 may be isolated from the circulation system by closure of the valves 43 and 44 and is provided with a drain conduit including a valve 52; the filter 22 may be isolated from the circulation systemv by cle-sure of the valvesf45 and 46 and is provided with a drain conduit includnga valve vr53; land 'the filter 23 may be isolated from the circulation system by closure of the valves 47 and 48 and is providedwith adrain conduitincluding a valve 54. The filters 20 and 21`may be identical,

j shown.

each containing a packing of activated carbon; and the filters 22 and 23 may be identical, each containing a packing of diatomaceous earth, etc.

The heater 12 comprises the inlet header 61 and an outlet header 62 interconnected by a number of tubes 63, as Well as a jacket 64 surrounding the tubes 63. The plating solution is circulated from the inlet header 61 through the tubes 63 to the outlet header 62 and therefrom into a branched conduit 55. The jacket 64 is provided with an inlet conduit 65 and an outlet lconduit 66; the inlet conduit 65 includes va valve 67 and is connected to a live steam pipe 68; while the outlet conduit 66 includes a valve 68 and extends to drain. One branch of the conduit 55 communicates with the regeneration tank 10 and includes a valve 56; another branch of the conduit 55 communicates with the plating tank 13 and includes a valve 57; and a further branch of the conduit 55 communicates with the plating tank 14 and includes a valve 58. v

The plating'tank 13 is adapted to contain a hot bath of the plating solution and is provided with an overtiow hood 71, as well as a bottom drain conduit 72 including a valve 73; and likewise, the plating tank 14 is adapted to contain a hot bath of the plating solution and is provided with an overliow hood 74, as Well as a bottom drain conduit 75 including a valve 76. A conduit 81 is provided that has two branches, one branch thereof communicating with the hood 71 and including a valve 84, and the other branch thereof communicating with the hood 74 and including a valve 85; and the conduit 81 communicates with the inlet of the pump 18, and the outlet of the pump 18 communicates with a conduit 86.

The cooler 16 comprises an inlet header 91 and an outlet header 92 interconnected by a number of tubes 93, as well as a jacket 94 surrounding the tubes 93. The conduit 86 is branched, one branch thereof including a valve 95 and vextending to drain, and the other branch thereof including a valve 96 and extending to the inlet header 91; whereby the plating solution is circulated from the inlet header 91 through the tubes 93 to the outlet header 92 and therefrom into a conduit 97. The jacket 94'is provided with an inletconduit 98 and an outlet conduit 99; .the inlet conduit 98 includes a valve 10i) and is connected to a cold water pipe'101; while the outlet conduit 99 includes a valve 102 and extends to drain. The conduit 97 extends back to the regeneration tank 1t) and includes a valve 103. Also a make-up conduit 104 communicates with the regeneration tank 16 and includes a valve 105.

A nitric acid line 111 communicates with the plating tank 13 and includes a valve 112;and likewise, a nitric acid line 113 communicates with the vplating tank 14 and includes a valve 114; which lines 111 and v113 are connected to a suitable source of dilute nitric acid, not

r[he bottom of the regeneration tank 19 communicates with a branched conduit 115, one branch j thereof including a valve 116 and extending to drain,

and the other branch thereof including a valve 117 and extending to the storage tank 11. Finally a by-pass conduit 120 is connected between the conduit 97, at the header 92 of the cooler 16, and the inlet of the pump 17; which by-pass conduit 120 includes a normally closed valve 121 and is employed for a purpose more fully explained hereinafter.

ln view of the foregoing, it will be understood that the plating solution inthe storage tank 11 may be circulatedby the pump 17 through either one of the filters 20 or 21, or around the filters 2t) and 21, from the header 34 tothe header 35; and then the plating solution may be circulated through either one of the iilters 22 or 23, or

Vheater 12 into the conduit 55` From the conduit 55, the

plating solution may-be -supplied.toveither-"one of the plating tanks 13 or 14 andtherefrom into the condint 81. From the conduit 81 thevplatingsolution is clrculated by the pump 18 through the cooler 16 and thence via the conduit 97 back to the regeneration tank 10. From the regeneration tank 10, the plating 4solution is returned via the conduit 115 to the storage tank 11.

YIn the storage tank 10, the plating solution may have a temperature of `about 609 C.; in the` heater 12,V the plating solution is heated to a temperature in the general range 85 C.to 95 C.; inthe active plating tank 13 or 14, a bath of-the plating solution is held at the relatively' high temperature in the range 85 C. tot-95 C.; and in the cooler 16, the temperature of the plating solution is reducedsubstantially back to 60 C. to be returned back tothe regeneration tank and thence to -the storage tank 1,1 -to complete the circuit of the circulated plating solution. In the heater 12, the heat is supplied from the'steam pipe 68', and in ,theV cooler 16, the heat is extracted by virtue of the supply thereto of the cold water from the cold water supply pipe 101.

In theoperation of the system, the ingredients of the plating solution arev depletedsomewhat in the active plating tank 13 or 14, whereby the plating solution is regeneratedin the regeneration' tank 10 by the supply of make-up ingredients from the make-up conduit 104, the ingredients normally being dissolved in appropriate aqueous solutions that are supplied via the make-up conduit 104 into the regeneration tank 10.

In the operation of the system normally one of the plating tanks 13 or 14 is active and the other of these plating tanks is inactive, the plating solution being supplied to the active plating tank, as previouslyr noted. On the other hand, the b'oat or filler 24 or 25 is placed in the inactive plating tank 13 or 14 so as to ll up a substantial proportionjof the volume thereof, whereupon the dilute solution of nitric acid is introduced into the inactive plating tank by opening of the associated valve 112 or 114 in the vassociated nitric acid line 111 -or 113. Accordinglya charge of dilute nitric acid (about 0.1 N) is held in the inactive platingV tank 13 or 14 for a suitable time interval in order to elect complete deactivation of the walls thereof. The time interval is not particularly critical, but should be suflicientlyY long to eiect the object mentionedand is normally at least about 8 hours. As a practical matter, in a two-.tank plating system, it is convenient to employ the plating tanks 13 and 14 alternatively; whereby each of the tanks is active for about twelve hours of the day and inactive for about 12 hours ofthe day, the l2-hour period being entirely adequate to insure complete deactivation of the walls of the inactive tank. The utilization of the boats 24 and 25 in conjunction with the plating tanks 13 and 14 is entirely optional, but the arrangement is very useful as it minimizes the charge ofV dilute nitric acid required completely to iill the associated plating tank when the boat is in place therein. l

Also, periodically (about every three weeks) all of the plating solution in the system is accumulated in the regeneration tank 10 and in the storage tank 11; the valves 33 and 103 are closed; and the valve 121 in the by-pass conduit 120 is opened. A charge of dilute nitric acid solution of the character noted is then introduced into one of the plating tanks 13 or 14, and circulated through the elements 18, 16, 17, 12 and 13 or 14.for a suitable time interval (normally about eight hours) so as to deactivate these elements. In this step the valves 41, 42, 43, 44, 45, 46, 47 and 48 are closed, and the valves 37 and 38 are opened, so that the nitric acid solution by-passes the filters 20, 21, 22 and 23, since there is no point in circulating the dilute nitric acid solution through these filters, as they are ordinarily cleaned and serviced daily anyway. This step is very desirable with respect to-theY heater 12, the cooler 16 and the.pumps 17 and 18; *and this step is ynot required more often, since the relatively'high velocity of the plating solution in the normal operation of the system seems to minimize the tendency to platelupon thefelements 12, 16, 17 and 18, and also since these elements do not contactv ,the

work-pieces, as do the plating tank- 13 and 14 from time to time in the loading and unloading thereof. Thus this step is similar to that involving the deactivation of the platingtanks 13 and 14, -but is not ordinarily so frequent, as previously explained. v

In conjunction'with the-deactivation of the stainless` steel elements 12, 13,14, 16, 1.7 and 18, it is noted that particularlyY good results'are achieved'in accordance with4 the present method, when these parts are formed of anyv one of the following stainless steels-that have been thoroughly tested and found Ato be highly satisfactory: S304,

S310, S316, S347 and S430. 'Y The plating solution, as previously noted, is of the nickel cation-hypophosphite anion type, and itl may take a wide variety of forms as disclosed in U. S. Patent No.

2,532,283, granted on December 5, 1950 to Abner Bren-l ner and Grace E. Riddell, U. S. Patent No. 2,658,841,

granted onA November 10, 1953 to Gregoire Gutzeit and Abraham Krieg, or U. S. Patent No. 2,658,842, granted on November 10, 1953 to Gregoire Gutzeit and Ernest I.' Ramirez. Preferably the plating solution is lof'the character of that disclosed in the copending application of Gregoire Gutzeit, Serial No. 376,977, filed August 27, 1953, the copending application of Gregoire Gutzeit, Paul lTalmey and Warren G. Lee, Serial No. 478,492, led

December 29, 1954, or the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Serial No. 569,815, tiled March', 1956. For example, such a chemical nickel plating solution essentially comprises an aqueous solution of nickel ions and hypophosphite ions,

-the solution normally containing an absolute concentra' tion of hypophosphite ions within the range 0.15 to 1.20 moles/liter and a molar ratio between nickel ions and hypophosphite ions within the range 0.25 to 1.60, and a pH within the range 4 to 11. More specifically, the plating solution disclosed in the Gutzeit, Talmey and Lee` application, Serial No. 569,815, comprisesan aqueous solution containing an absolute concentration of hypophosphite ions within the range 0.15 to 1.20 moles/liter, a molar ratio between nickel ions and hypophosphite ions within the range 0.25 to 1.60, an absolute concentration of lactic ions within the range'0.25 to 0.45 mole/liter, an absolute concentration of propionic ions within the range 0.025 to 0.045 mole/liter, and a pH within the range 4.4 to 5.6. A specific preferred example of this plating solution has the following composition:

Moreover, the selected chemical nickel plating solution contains a stabilizing amount of a stabilizer, as disclosed in the previously mentioned Talmey and Gutzeit Patent No. 2,762,723, and lead ion is particularly recommended as it is both very economical and easy to control in the plating process, and of course the lead ion stabilizer is Very eiective to prevent random decomposition of the plating solution. The lead ion content of the plating solution in parts-per-million of the solution by weight is normally within the range 1 to 5 p. p. m. More particularly, the plating solution employed contains a stabilizing amount of stabilizer corresponding to the maximum stabilizer concentration therein that is compatible with both a high plating rate thereoffand complete plating coverage of the work-pieces being plated. This vsta bilizing amount of the stabilizer can bereadily established by running a curve upon the given plating solution .containing the particular stabilizer, plotting'athe .platingl rate of the plating solution against the stabilizer content thereof, whereby the stabilizing amount of the stabilizer will ordinarily be selected to correspond to the stabilizer concentration in the plating solution that is productive of a depression of about to 10% in the maximum plating rate thereof. yl

This step of establishing the stabilizing amount of the particular stabilizer in the given plating bath will be readily understood from an examination of Fig. 2 of the drawings, wherein the particular stabilizer employed is l lead ions and the given plating solution has the composition of that previously set forth. From the curve of Fig. 2, it will be observed: this plating solution of the composition set forth has a plating rate as prepared of 0.950 mil/hr.; upon the addition thereto of 1 p. p. m.

of lead ions, the plating rate thereof is boosted to 1.000 mil/hr.; upon the addition thereto of 2 p. p. m. of lead ions, the plating rate thereof is depressed to 0.950 mil/ hour; upon the addition thereto of 3 p. p. m. or lead ions, the plating rate thereof is depressed to 0.688 mil/ hr.; upon the addition thereto of 4 p. p. rn. of lead ions, the plating rate thereof is depressed to 0.338 mil/ hour; and upon the addition thereto of 5 p. p. m. of lead ions, the plating rate thereof is depressed to 0.131 mil/hour.

Accordingly, in accordance with the present method, the stabilizing amount of this particular stabilizer (lead ions) that should be employed in this given plating solution of the composition set forth is within the approximate range 11/2 to 21/2 p. p. m., a lead ion concentration of 2 p. p. m. being generally quite satisfactory.V

With further reference to the matter of the stabilizing amount of the particular stabilizer that should be employed in a given plating solution, it is mentioned that different plating solutions are sensitive over a wide range to a particular stabilizer, and that a given plating solution is sensitive over a wide range to different stabilizers; whereby it is necessary to run a curve upon the given plating solution in conjunction with the particular sta bilizer in order to establish the proper stabilizing amount of the particular stabilizer that should be employed in the given plating solution so as to obtain the desired depression of .about 5% to 10% in the maximum plating rate of the given plating solution. Moreover the matter of selecting the range of the depression of about 5% to of the maximum plating rate of the given plating solution is also largely a matter of convenience in operating the plating process, since it will be appreciated that satisfactory operation can be obtained utilizing a given plating solution containing a particular stabilizer such that the maximum plating rate is depressed by an amount extending Lbeyond either end of the range mentioned. Or" course, the utilization of a given plating solution in which the maximum plating rate is depressed substantially in excess `of about 10% is ordinarily objectionable from a consideration of plating production in a continuous chemical nickel plating system, while the utilization of the given plating solution in 'which the maximum plating rate is depressed substantially less than 5% is ordinarily objectionable from a consideration of the plating solution stability with respect to random decomposition and from a consideration of complete elimination of random plating upon the elements of the plating system. ln other words, to prevent the random nickel plating upon the plating tank, and other component parts of the system, the combination of steps previously described is required; which combination includes the step involving the utilization of the given plating solution containing the stabilizing amount of the particular stabilizer.

As previously explained, the lead ions, as a stabilizer, is specifically recommended, and an improved method of formulating a chemical nickel plating bath of the nickel cation-hypophosphite anion type containing the desired stabilizing amount of lead ions is disclosed in the copending application of Paul Talmey and Glenn Enyart7 Serial No. 695,127, filed November 7, 1957, and this method of formulating the bath is also recommended from a commercial standpoint. v

Hence, in accordance with the present method, the given plating solution that is to be employed is formulated containing the stabilizing amount of the particular stabilizer and then utilized in the plating process in the manner previously described. As the plating process proceeds, the ingredients of the plating solution are depleted; whereby it is necessary to regenerate the plating solution in the regeneration tank 10 of Fig. 1, either periodically or continuously, as desired. This regenera tion of the plating solution includes the utilization of an aqueous stock'solution of the particular stabilizer. For example, utilizing lead ions, an aqueous solution of lead nitrate is recommended. Of course, the plating solution is also regenerated with respect to nickel cations and hypophosphite anions, as well as the other ingredients thereof (lactic ions and propionic ions and lead ions in the example set forth); and moreover, hydroxyl anions are added thereto in order to preserve the desired pH thereof, as it will be understood that the nickel reductionhypophosphite oxidation reaction is productive of hydrogen cations, resulting in a reduction -of the pH of the plating solution in the absence of pH control.

As previously noted, the regeneration of the plating solution is effected under good agitation in the regeneration tank 10, from which it is transferred to the storage tank 11 and thence delivered by the pump 17 via the lter system to the heater 12. Following regeneration, it is recommended that the plating solution be circulated through one of the activated carbon lters 20 and21 for a short time interval and thence continuously through one of the polishing lters22 or 23. The continuous circulation of the plating solution through one of the activated carbon filters 20 or 21 is not necessary; and moreover, such continuous circulation of the plating solution through vone of the activated carbon iilters 20 or 21 effects the removal of the lead ion stabilizer there from progressively as time proceeds in an undesirable manner. On the other hand, the continuous circulation of the plating solution through one of the polishing filters 22 or 23 is recommended, as this step insures that no line insoluble materials are suspended in the plating solution that might be productive of random decomposition of the plating solution. Further, it is mentioned that the arrangement of the ilter system preceding the heater 12 is very advantageous, as it is desirable to filter the plating solution while it is at a relatively low temperature, since any solid materials suspended in the plating solution are soluble to a minimum degree at the relatively low temperature, thereby positively insuring that there are no solid materials suspended in the plating solution following the heating thereof in the heater 12 to the relatively high temperature and incident to the delivery thereof to the active plating tank 13 or 14.

Of course, the work-pieces that are plated in the plating tanks 13 or 14 must have catalytic surfaces; and it will be understood that the c aalytic elements are cobalt, nickel, palladium, rhodium and ruthenium. However, a large number of other elements can be rendered catalytic, either by displacement or by galvanic initiation in the plating solution, so that the autocatalytic plating reaction may proceed; which elements include aluminum,

carbon, copper, iron, magnesium, titanium and uranium l (as well as silver and gold), and the various alloys thereof. Also, insulators can be satisfactorily nickel plated when the surfaces thereof are suitably activated with one of the catalytic elements named.

Moreover, in the plating of the work-pieces in the plating tank 13 or 14, it is important that they be immersed in the plating solution and out-of-contact with the walls of the plating tank 13 or 14, since contact between a work-piece and a wall of the plating tank has a tendency to set-up an undesirable galvanic current there- Y chamber between successive be'eenycausing plating.: pon-.the .walltofthe plating ta a Thel present,

vInthe operation of thewplating system, it is recom. mended that the ow or circulation of the plating solution .therethrough be at a relatively high rate, as this consideration also has a tendency Ato prevent random nickel plating in the heater 12.' For example, the rate ofv liow of the plating'solution in the plating system should be such that the hot bath thereof held in the active plating tank 13 or 14 is completely renewed every two or three minutes.`

In view of the foregoing, it is apparent that there has been provided an improved method of continuous chemical` nickel plating utilizing a chemical nickel plating solution of the `nickel cation-hypophosphite anion type in which random nickel plating upon .the plating tank and other component parts of the system is avoided.

While there khas been .described what'is at present considered to be the preferred embodiment of thel invention, it will be understood that various modifications may be made therein, and-'it is intended vto cover in the appended claims all such modifications as vfall within the true spirit and scope of the invention.

Whatis claimed'is: a

, 1.y The method` of chemical nickel plating comprising providing a chemical nickel plating solution of the nickel cation-hypophosphiteanion typ'e containing a stabilizing amount of leadion therein, providinga plating chamber defined by wallsformedsof steel containing a high chromium content, deactivating substantially periodically the steel walls ofsaid plating chamber by treatment with a dilute nitric acid solution, holding a hot'bath of the plating solution in saidy plating chamber in thetim'e intervals between successive deactivations of the steel Walls thereof, maintaining the hot bath held in said plating chamber atA a temperature not in excess of '95' C., immersing workpieces tobe plated in the hot bath held in said plating chamber and out-of-contact with'the steel walls thereof, saidstabilizing amountl of lead ion contained in the plating solution being ,in the range lfto p. p. m; of the plating solution by weightand corresponding to the maximum lead ion concentration therein that is compatible with both a high plating rate of the hot bath and complete plating coverage of the work-pieces, and maintaining said stabilizing amount of lead ion in the plating lsolution by adding lead ions thereto asthe plating ofthe work-pieces proceeds in the hot bath held in saidplating chamber.

2. The method set forth in claim 1, wherein the steel walls of said plating chamber are deactivated by recirculation of the dilute,- .nitric a-cid solution therethrough.

3. The method rset forth in claim l, wherein the steel walls of said plating chamber are'deactivated by soaking in a charge of the dilute nitric acid solution held therein.

4. The method set forth in claim 1, wherein the time interval during which the hot bath is held -in said plating deactivations of the steel walls thereof is not in excess of one day.

5. The continuous method ofhemical nickel plating comprising providing a chemical nickel plating solution of the nickel cation-hypophosphite.anion type containing a stabilizing tracel amount of lead ion therein, providing a plating chamberdeined by walls formed of steel containing a high by treatment with a dilute nitric -acid solution, holding'a hot bath of the plating solution in `said. platingchamber successive deactivations of` chromium content, :deactivating substan tially periodically the steel walls of said plating chamberv perature but not in excess of thence back into said plating chamber, heating the plating solution in said heater. to a relatively high temperature but not inexcess of f C., cooling the plating solution in said cooler to a relatively low temperature well below 95 C., immersing work-pieces to .be plated inthe hot bath held in said plating chamber and out-of-contact with the steel walls thereof, said stabilizing amount. of lead ion contained in the plating solution being in the range.

l to 5 p. p. m. of the plating solution by weight and corresponding to the maximum lead ion concentration therein that is compatible with both a high plating rate of thev hot bath and complete plating coverage of the work-pieces, and regenerating the circulated plating solution with respect to the ingredients thereof, wherein said last-mentioned step includes adding suicient lead ions to the plating solution to lmaintainsaid stabilizing amount of lead ions therein. v

6. The continuous method of chemical nickel plating comprising providing a chemical nickel plating solution of the `nickel cation-hypophosphite anion type containing a stabilizing trace amount of lead ion therein, providing a plating chamber Vdefined by walls formed of steel containing a high chromium content, deactivating substantially periodically .the steel walls of said plating chamber by treatment witha dilute nitric acid solution, holdinga hot bath of the plating solution in said plating chamber in the time intervals between successive deactivations of the steel walls thereof, continuously circulating the plating solutionof the bath held in said plating chamber therefrom through a cooler and then through a heater and thence back into said plating chamber, heating the plating solution in said heater to a relatively high tem solution in said -cooler to a relatively low te-mperature well below 95 C., immersing workfpieces to be plated bath held in said plating chamber and out-of-`A in the hot y contact with the steel Walls thereof, said stabilizing amountof lead ion contained in the plating solution being inthe'ra'nge 1 'to 5 p. p. m.'of the plating solution by weight and corresponding to the maximum lead ion concentration therein that is compatible with both a high plating rate ofthe hot bath and complete plating coverage of the Workepieces, continuously filtering the circulated plating solution in a filter disposed ahead of said heater, and regenerating the circulated plating solution with respect'to the ingredients thereof by adding such ingredients thereto ahead of said filter, and maintaining said stabilizing amount of 'lead ion in the plating solution by adding lead ions thereto as the plating of the work-pieces proceeds in the hot bath held in said plating chamber.

7.,The continuous method of chemical nickel plating comprising providing a chemical nickel plating solution of the' nickel cation-hypophosphite anion type containing a stabilizing trace amount of lead ion therein, providing a plating tank and a cooler and a heater each having ywalls adapted to contact the plating solution and formed offsteel having a high chromium content, deactivating substantially periodically the steel walls of said plating tankfbyj contacting them with a dilute nitric acid solution, holding a hot bath of the plating solution in said plating tank in the time intervals between successive deactivations of the steel walls thereof, continuously circulating the plating solution of the bath held in said plating chamber IwithV the steel walls, thereof, deactivating substantially periodically the steel wallsof said heater and of said cooler by contacting themwith a dilute nitric acid solution, said stabilizing amount of lead ion contained in the plating solution being inthezrauge l to 5 p. p. m. of the 95 C., cooling the plating` plating solution by weightV and corresponding to the maximum `lead ion concentration therein that is compatible with both a high plating rate of the hot bath and complete plating coverage v'of the work-pieces, and regenerating the circulated plating solution with respect to the ingredients thereof, wherein said last-mentioned step includes adding suicient lead ions to the plating solution to maintain said stabilizing amount of lead ions therein.

8. The method set forth in claim 7, wherein the steel walls of said heater and said cooler are deactivated by recirculation of the dilute nitric acid solution therethrough.

9. The method set forth in claim 7, wherein the steel walls of said plating tank are deactivated about once during each period of one day and the steel walls of said heater and of said cooler are deactivated about once during each period of three weeks.

10. The continuous method of depositing nickel from a chemical reduction plating solution of the nickel cationhypophosphite anion type, comprising formulating the plating solution with respect to the desired ingredients thereof and including a stabilizing amount of lead ion therein, providing a plating chamber defined by walls formed of steel containing a high chromium content, deactivating substantially periodically the steel walls of said plating chamber by treatment with a dilute nitric acid solution, holding a hot bath of the plating solution in said plating chamber in the time intervals between successive deactivations of the steel walls thereof, said stabilizing amount of lead ion contained in the plating solution being in the range l to'5 p. p. m. of the plating solution by weight and being in excess of the lead ion concentration therein that is productive of the maximum plating rate of the hot bath thereof and corresponding to the lead ion concentration therein that is productive of a depression of about to 10% in the maximum plating rate'of the hot bath thereof, continuously circulating the plating solution of the bath held in said plating chamber therefrom to the exterior and then back thereinto, heating the circulated plating solution to a relatively high temperature not in excess of 95 C. exteriorly of said plating chamber and before it is introduced thereinto, cooling the circulated plating solution to a relatively low temperature well below 95 C. exteriorly of said plating chamber and after it is withdrawn therefrom, immersing articles to be coated in the -hot bath held in said plating chamber, and regenerating the plating solution with respect tothe ingredients thereof, wherein said last-mentioned step includes adding sufficient lead ions thereto to maintain said stabilizing amount of lead ions therein.

il. The continuous method of depositing nickel from a chemical reduction plating solution of the nickel cationhypophosphite anion type, comprising formulating the plating solution with respect to the desired ingredients thereof and including a stabilizing amount of lead ion therein, providing a plating chamber defined by walls formed of steel containing. a high chromium content, deactivating substantially periodically the steel walls of said plating chamber by treatment with a dilute nitric acid solution, holding a hot bath of the plating solution in said plating chamber in the time intervals between successive deactivations of the steel walls thereof, said stabilizing amount of lead ion contained in the plating solution being in the range 1 to 5 p. p. m. thereof by weight and corresponding to a lead ion concentration therein of about l/2 p. p. m. thereof above the lead ion concentration therein that is productive of the maximum plating rate of the hot bath, continuously circulating the plating solution of the bath held inl said plating chamber therefrom to the exterior and then back thereinto, heating the circulated plating solution to a relatively high temperature not in excess of 95 C. exteriorly of said plating chamber and before it is 'introduced thereinto, cooling the circulated plating solutionto a relatively low temperature well below 95 C. exteriorly of said plating chamber and after it is Cit withdrawn therefrom, immersingarticles .to lbe coated n the hot bath held in said plating chamber, and regenerating-the.platingsolution with respectto the ingredients thereof, wherein said last-mentioned step includes adding sufficient lead ions thereto to maintain said stabilizing amount of lead ions therein.

l2. The continuous method of depositing nickel from a chemical nickel reduction plating solution of the nickel cation-hypophosphite anion type,icomprising formulating the plating solution with respect to the desired ingredients thereof and including a stabilizing amount of a selected stabilizer therein., vrproviding a plating chamber defined by walls formed of steel containing a high chromium content, deactivating substantially periodically the steel walls of said plating chamber by treatment with a dilute nitric acid solution, holding a hot bath of the plating solution in said plating chamber in the time'intervals between successive deactivations of the steel walls thereof, said stabilizing amount of said selected stabilizer contained in the plating solution being adequate to prevent spontaneous decomposition of the hot bath thereof'l and being in the rangeof parts-per-million of the plating solution. by weight and also being bilizer concentration therein that maximum plating rate of the hot ther corresponding to the stabilizer that is produetivefof a ,depression of about 5% to 10% in the maximum plating rate of the hot bath thereof, continuously circulating the plating solution of the bath held in said plating chamber therefrom to the exterior and then back thereinto, heating the circulated plating solution to a relatively high temperature not in excess of C. exteriorly of said :plating chamber and before it is introduced thereinto, cooling the circulated plating solution to a relatively low temperature well below 95 C. exteriorly of `said plating chamber and after it is withdrawn therefrom, immersing articles to be coated in the hot bath held in said plating chamber, and regenerating the plating solution with respect to the ingredients thereof, wherein saidlast-mentioned step includes adding a suicient amount of said selected stabilizer to the plating solution to maintain said stabilizing amount of said selected stabilizer therein.

l3. The continuous method of depositing nickel from a chemical nickel reduction plating solution of the nickel cation-hypophosphite anion type, comprising formulating the plating solution with respect to the desired ingredients thereof and including a stabilizing amount of a selected stabilizer therein, providing two plating chambers each defined by walls formed of steel containing a high chromium content, alternately holding a hot bath of the plating solution in the active one of said plating chambers and deactivating the steel walls of the inactive other of said plating chambers, wherein said deactivation is effected by treatment with a dilute nitric acid solution, said stabilizing amount of said Selected stabilizer contained in the plating solution being adequate to prevent spontaneous decomposition of the hot bath thereof and being in the range of parts-per-million of the plating solution by weight and also being in excess of the stabilizer concentration therein that is productive of the maximum plating rate of the hot bath thereof and further corresponding to the stabilizer concentration therein that is productive of a depression of about 5% to 10% in in excess of the stais productive of the bath thereof and furconcentration therein the maximum plating rate of the hot bath thereof, continuously circulating the plating solution of the bath held in the active one of said plating chambers therefrom to the exterior and then back thereinto, heating the circulated plating solution to a relatively high temperature not in excess of 95 C. exteriorly of the active one of saidplating chambers and before it is introduced thereinto, cooling the circulated plating solution to a relatively low temperature well below 95 C. exteriorly of the active one of said plating chambers and after it is withdrawn therefrom, irnmersing articles to vbe coated in the hot bath held in the active one of said plating chambers, and regenerating the plating solution with respect to the ingredients thereof, wherein said last-mentioned step includes adding a suiiicient amount of said selected stabilizer to the plating solution to maintain said stabilizing amount of said selected stabilizer therein, and wherein said alternation of said plating chambers is not more frequent than several hours so as to insure that the dilute nitric acid solution held in the inactive one of said plating chambers has suiicient time to effect complete deactivation of the steel wallsthereof.

14. The continuous method of depositing nickel from a chemical nickel reduction plating solution of the nickel cation-hypophosphite anion type, comprising formulating the plating solution with respect to the desired ingredients thereof and including a stabilizing amount of a selected stabilizer therein, providing a plating chamber defined by Walls formed of steel containing a high chromium content, deactivating substantially periodically the steel walls of said plating chamber by treatment with a dilute nitric acid solution, holding a hot bath of the plating solution in said plating chamber in the time intervals between successive deactivations of the steel walls thereof, said stabilizing amount of said selected stabilizer contained in the plating solution being adequate to pre vent spontaneous decomposition of the hot bath thereof and being in the range of parts-per-rnillion of the plating solution by weight and also being in excess of the stabilizer concentration therein that is productive of the maximum plating rate of the hot bath thereof and further corresponding to the stabilizer concentration therein that is productive of a depression of about to 10% in the maximum plating rate of the hot bath thereof, continuously circulating the plating solution of the bath held in said plating chamber therefrom to the exterior and then back thereinto, heating the circulated plating solution to a relatively high temperature not in excess of 95 C. exteriorly of said plating chamber and before it isintroduced thereinto, cooling the circulated plating solution to a relatively low temperature Well below 95 C. exteriorly of said plating chamber and after it is withdrawn therefrom, immersing articles to be coated in the hot bath held in said plating chamber, regenerating the plating solution with respect to the ingredients thereof by adding thereto aqueous solutions of the ingredients, saidA last-mentioned step including adding a suflicient amount of said selected stabilizer to the plating solution to maintain said stabilizing amount of said selected stabilizer therein, and extracting suflicient Water vapor from the plating solution to prevent substantial variation of the volume thereof notwithstanding said additions thereto of said aqueous solutions of the ingredients thereof.

15. The method of chemical nickel plating comprising providing a chemical nickel plating solution of the nickel cation-hypophosphite anion type containing a stabilizing amount of a selected stabilizer therein, providing a plating chamber defined by Walls formed of steel containing a high chromium content, deactivating substantially periodically the steel walls of said plating chamber by treatment with a dilute nitric acid solution, maintaining a hot bath of the plating solution at a temperature not in excess of 95 C. in said plating chamber in the time intervals between the successive deactivations of the steel Walls thereof, immersing work-pieces having catalytic surfaces to be plated in the hot bath in said plating chamber and out-of-contact with the steel walls thereof, said stabilizing amount of said selected stabilizer said selected stabilizer in contained in the plating solution being adequate to prevent spontaneous decomposition of the hot bath thereof and also being in the range of parts-per-million of the plating solution by Weight and further corresponding to the maximum stabilizer concentration therein that is compatible with both a high plating rate of the hot bath and complete plating coverage of the catalytic surfaces of the work-pieces, and maintaining said stabilizing amount of said selected stabilizer in the plating solution by adding said selected stabilizer thereto as the plating of the catalytic surfaces of the work-pieces proceeds in the hot bath.

16. The method set forth in claim 15, wherein the hot bath has a temperature in the range C. to 95 C.

17. The method set forth in claim 15, wherein said bath as formulated comprises an absolute concentration of hypophosphite ions within the range 0.15 to 1.20 moles/liter and a molar ratio between nickel ions and hypophosphite ions within the range 0.25 to 1.60 and a pH within the range 4 to 11.

18. The method set forth in claim 15, wherein said bath as formulated comprises an absolute concentration of hypophosphite ions Within the range 0.15 to 1.20 moles/liter and a molar ratio between nickel ions and hypophosphite ions within the range 0.25 to 1.60 and an absolute concentration of lactic ions Within the range 0.25 to 0.45 mole/ liter and an absolute concentration of propionic ions within the range 0.025 to 0.045 mole/ liter and a pH within the range 4.4 to 5.6.

19. The method set forth in claim 15, wherein said stabilizer consists essentially of heavy metal ions.

20. The method set forth in claim 15, wherein. said stabilizer consists essentially of a thio compound that is soluble in said bath.

n 21. The method of chemical nickel plating comprising providing a chemical nickel plating solution of the nickel cation-hypophosphite anion type containing a stabilizing amount ofV a selected stabilizer therein, providing a plating chamber dened by walls formed of stainless steel, deactivating substantially periodically the stainless steel walls of said plating chamber by treatment with a dilute nitric acid solution, maintaining a hot bath of the plating solution at a temperature not in excess of C. in said plating chamber in the time intervals between the successive deactivations of the stainless steel walls thereof, immersing work-pieces having catalytic surfaces to be plated in the hot bath in said plating chamber and outof-contact with the stainless steel walls thereof, said stabilizing amount of said selected stabilizer contained in the plating solution being adequate to prevent spontaneous decomposition of the hot bath thereof and also being in the range of parts-per-million of the plating solution by weight and further corresponding to the maximum stabilizer concentration therein that is compatible with both a high plating rate of the hot bath and complete plating coverage of the catalytic surfaces of the work-pieces, and maintaining said stabilizing amount of the plating solution by adding said selected stabilizer thereto as the plating of the catalytic surfaces of the work-pieces proceeds in the hot bath.

References Cited in the le 'of this patent UNITED STATES PATENTS 2,726,969 Spaulding Dec. 13, 1955 

1. THE METHOD OF CHEMICAL NICKEL PLATING COMPRISING PROVIDING A CHEMICAL NICKEL PLATING SOLUTING OF THE NICKEL CATION-HYPOPHOSPHITE ANION TYPE CONTAINING A STABILIZING AMOUNT OF LEAD ION THEREIN, PROVIDING CHAMBER DEFINED BY WALLS FORMED OF STEEL CONTAINING A HIGH CHROMIUM CONTENT, DEACTIVATING SUBSTANTIALLY PERIODICALLY THE STEEL WALLS OF SAID PLATING CHAMBER BY TREATMENT WITH A DILUTE NITRIC ACID SOLUTION, HOLDING A HOT BATH OF THE PLATING SLUTION IN SAID PLATING CHAMBER IN THE TIME INTERVALS BETWEEN SUCCESSIVE DEACTIVATIONS OF THE STEEL WALLS THREREOF, MAINTAINING THE HOT BATH HELD IN SAID PLATING CHAMBER AT A TEMPERATURE NOT IN EXCESS OF 95*C., IMMERSING WORKPIECES TO BE PLATED IN THE HOT BATH HELD IN SAID PLATING CHAMBER AND OUT-OF-CONTACT WITH THE STEEL WALLS THEREOF, SAID STABILIZING AMOUNT OF LEAD ION CONTAINED IN THE MAXIING SOLUTION BEING IN THE RANGE 1 TO 5 P. P. M. OF THE PLATING SOLUTION BY WEIGHT AND CORRESPONDING TO THE MAXIMUM LEAD ION CONCENTRATION THEREIN TAHT IS COMPATIBLE WITH BOTH A HIGH PLATING RATE OF THE HOT BATH AND COMPLETE PLATING COVERAGE OF THE WORK-PIECES, AND MAINTAINING SAID STABILIZING AMOUNT OF LEAD ION IN THE PLATING SOLUTION BY ADDING LEAD IONS THERETO AS THE PLATING OF THE WORK-PIECES PROCEEDS IN THE HOT BATH HELD IN SAID PLATING CHAMBER. 